Head-mounted display devices offer the promise of enabling new human-computer interaction paradigms in a variety of fields such as gaming, aviation, engineering, science, and medicine, through a wearable device that is convenient for the user to selectively engage. One constraint with such devices, however, is that the human eye cannot focus on a point source located approximately 10 centimeters (cm) or less away from the eye. For this reason, head-mounted displays may utilize optical elements or waveguides in front of the eye, which results in a thicker and more bulky device than is desired. In these devices, user comfort, device mobility, and device aesthetics are often compromised.
Another possible display system for head-mounted display devices is a retinal scanning laser. Such a solution may also utilize elements in front of the eye, such as a mirroring surface, waveguide, or a steerable mirror. One example may be a laser diode mounted near a user's temple to direct a light beam to a steerable micro-mirror that scans the beam. The scanned beam may be reflected via one or more other mirrors into the eye. In another example, the steerable micro-mirror may be positioned in front of the eyes and may reflect the beam directly into the eyes.
A problem with locating a steerable micro-mirror in front of the eye is that it limits the user's field of view, since a mirror near the eye has to be relatively large to cover the range of rotation of the eye. Devices with a laser diode mounted near the temple suffer a similar problem, in that the mirroring surface is necessarily strongly convex to enable the beam to enter the pupil from a wide range of angles. Such a constraint is difficult to address for a range of pupil positions. This is especially true given the possibility of occlusion of the beam by the user's head.
Another possibility may be to use a non-standard lens-type such as a Fresnel lens. However, Fresnel senses are designed for use by a viewer that is far away relative to the diameter of the lens. Lenticular lenses or lens arrays may also be considered. Lenticular lenses are typically utilized to provide an angular dependence and stereo effect to prints. Lenticular printing works for distances at which the eye can focus, but adds an angular dependency, typically in the horizontal direction. Furthermore, if viewing is attempted from a close range, the image would be blurry at least in the vertical direction.